I just moved and I had to wait a few days for the cable guy to show up, so I busted out some of my old DVDs. I noticed that a couple of them were skipping scenes and/or freezing on a particular frame. A while ago I asked a kid at Blockbuster what he was cleaning their DVDs with and he flashed me a bottle of Windex. I was out of Windex, but I had some Fantastik and it worked just as well. No more skips or freezes.
TIP: Spray a little on a clean paper towel, clean in circles around the disc and dry (fully) with (dry) paper towel.